1. Field of the Invention
The present invention relates to a thermoplastic resin composition having excellent resistance to organic solvents and mechanical strength. Particularly, the present invention relates to a resin composition which is produced by mixing a polyphenylene ether resin with an unsaturated copolymer resin composed of an .alpha.-olefin and a diene so as to decrease reductions in impact resistance, which, in general, easily occur in incompatible resin mixtures, while barely reducing heat resistance and mechanical strength, both of which are characteristics of polyphenylene ether resins, and the moldability and resistance to organic solvents, both of which are characteristics of polyolefin resins. The resin composition is used as a molding material satisfying high quality requirements for structural members or the like of automobiles and electrical products.
2. Description of the Related Art
Although polyphenylene resins are useful as molding material resins because they have excellent thermal, mechanical and electrical properties, they have disadvantages with respect to processability, resistance to organic solvents and impact resistance and are thus limited in application range. A method of overcoming these disadvantages is disclosed in U.S. Pat. No. 3,383,435 in which the moldability is improved by mixing another resin, e.g., a styrene copolymer. However, this method cannot improve the resistance to organic solvents at all.
On the other hand, various blends with polyolefins having excellent resistance to organic solvents have been investigated, and a blend of polyolefin and a polyphenylene ether resin has been proposed in Japanese Patent Publication No. 42-7069. However, none of the blends sufficiently satisfy the high levels of mechanical strength required in industrial fields. In addition, Japanese Patent Laid-Open Nos. 53-71158, 54-88960 and 59-100159 disclose methods of adding, for example, a block copolymer of styrene and butadiene or a hydrogenation product thereof to a mixture of polyphenylene ether resin and polyolefin for the purpose of improving the compatibility therebetween. However, in these methods, since only small amounts of polyolefin are mixed, the polyphenylene ether resins form a substantially continuous phase, and the resistance to organic solvents possessed by the polyolefins is not sufficiently exhibited. Further, Japanese Patent Laid-Open Nos. 58-103557 and 60-76547 disclose compositions containing a polyphenylene ether resin, at least 20% by weight of polyolefin and a compatibilizing agent such as a diblock copolymer composed of an alkenyl aromatic compound and a conjugated diene, or a hydrogenation product thereof. Although the tensile properties and impact resistance of the compositions are improved, the rigidity and heat resistance thereof do not sufficiently satisfy the required levels.
One of the inventors previously found that a propylene-dialkenylbenzene copolymer which was modified with a styrene monomer and which was obtained by polymerizing, in the presence of a radical polymerization initiator, a styrene monomer with a crystalline propylene-dialkenylbenzene copolymer which was obtained by copolymerizing propylene as a main component and a small amount of alkenylbenzene compound is effective as a modifier for the affinity of a composition containing polyphenylene ether and polypropylene resins. The propylene-dialkenylbenzene copolymer is disclosed in Japanese Patent Laid-Open No. 1-170647.
However, the propylene-dialkenybenzene copolymer modified with a styrene monomer and obtained by copolymerization with a styrene monomer under conditions for radical polymerization is unsatisfactory in the addition effect of styrene. If styrene is added in an amount sufficient for an affinity modifier, although the impact strength is improved, there is the problem that the rigidity, particularly high-temperature rigidity, is reduced due to an increase in the polystyrene component. There is thus a demand for further improving the copolymer.